Method of preparing metal for painting



Patented Dec. 22; 1931 UNITED STATES PATENT OFFICE JAMES H. cnAvELL, or Enxms PARK, PENNSYLVANIA, ASSIGNOR 'ro AMERICAN CHEMICAL PAINT comm, or ,AMLBLER, rmsYLvAnIA, A CORPORATION or DE AWARE No Drawing.

This invention relates to theart of preparing metal for receiving an adherent finishing cost'and although it has various applications it will be found particularly useful for preparing sheet steel articles, such for instance as automobile bodies, fenders and stampings for receiving cellulose lacquer finishes.

This invention has among its objectsto clean the metal, to remove rust, scale, grease, oil, acids, soldering fluids, dirt, etc. from the surface of the metal, to produce a coating on the metal to which the lacquer or other finish will adhere, to so treat the metal that the use coating the steel or other metal with phos-.

phoric acid, permitting the said acid to chemically act on the metal to form a coating of soluble iron or other metallic phosphate and rendering the said'coating adherent and insoluble in water.

lVhen phosphoric acid is applied to the metal in the cold, its action on the metal is very slow andmany hours may elapse before a. noticeable coating of the soluble iron phosphate is developed. If the metal is heated after it has been coated with phosphoric acid, a satisfactory coating will develop-in a few minutes.

As the metal to be finished is usually, either through accident or designfcoated wlth oil,

it is difficult tocoat the metal with phosphoric acid, and even if this is accomplished, the coating .of oil 'beneath the coating of phosphoric acid prevents the acid from chemically acting on themetal to any material extent. Hence it is necessary to provide some way to assist the acid to chemically act upon the metal being treated. This may be done by first washing theametal with an oil removin material such for instance, as a solution 0 caustic soda or a solution of tri-sodium phosphate orthe metal may first be heated to a neuron or PREP RING METAL ron IPAIIN'TING Application -fi1 ed October 2, 1928. Serial No. 309,903.

temperature suflicient to burn ofi' the oil.

3 However the preferred method is to admix with the phosphoric acid an oil solvent, such for instance as an alcohol; a keystone, an ester or an ether, which will enable the acid admixture to penetrate the oil coating and thus permit the acid to chemically act on the metal. In practice an admixture of phosphoric acid, ethyl alcohol and butyl alcohol has been found to be a satisfactory mixture.

The coating developed by the action of the phosphoric acid is damp, non-adherent and soluble in water, due probably to the pres- 'ence of much free phosphoric acid. Such av coating is not suitable to paint over so that in order to convert it to a suitable coating it is treated with a material adapted to neutralize the phosphoric acid. Any proper material may be used for the purpose but slaked lime is considered'preferable. ther materials suches zinc oxide, tin oxide, magnesium oxide, calcium carbonate, magnesium carbonate may be .used as. the neutralizer however and satisfactory results obtained. The lime may be dusted over the surface although it is preferred to use it in the form of a viscous or semi-fluid whiteewash or paint produced byadmixing the lime with water, cellulose pulp waste liquor and butyl alcohol.

Unless a very rough or crude finish is desired the material adapted to neutralize phos phoric acid, together with the deleterious products'of its reaction, should be removed before the finish is applied. This may be accomplished by thoroughly washing the surface with water but where lime paint is used if it is permitted to dry on the surface it tends to crack and peel and is easily removed by simply brushing.

In thecase of steel, to carry out my process commercially good results are obtained by spraying the metal to be treated with an admixture comprising approximately; the following proportions: G u

' l 8. 011B Denatured alcohol. .70 Butyl alcohol .20 Phosphoric acid (75%) L .10

the'proportion of alcohol varying according to its purity and efiectiveness as an oil solvent.

In case all oil has been previously remove from the metal the alcohols may be dispensed with and a suitable admixture of water and phosphoric acid be substituted, using more or less thesame proportion of acid according to the rapidit of the action desired.

The metal is there ore placed in an oven heated to approximately 250 F. for a period of about fifteen minutes whereby a coating of soluble iron phosphate containing more or less free phosphoric acid will be developed. The metal is then removed from the oven and permitted to cool, after which it is sprayed or otherwisepoated with a viscous or semi-fluid material which is an admixture comprisin the following niaterials in approximate y the proportions stated:

Water .92(l"gallons Evaporated cellulose pulp waste liquor 1.110 pounds Quicklime 1.070 pounds Butyl alcohoL"; .050 gallons The coating is therefore permitted to during which time it absorbs an oil that may be present on the metal. As t e coating dries it cracks and peels and when it has become entirely dry it is ready to be removed.

This may be accomplished by brushing, preferably with a vacuum brush to avoid all dust. The coating thatis removed comprises lime, neutralized phosphoric acid and such oil as was present on the metal, and in fact all deleterious products of the chemical reac- 'tions of the process.

The resultant coating produced on the metal has a dull gray mat appearance and may be readily washed withwater without dangerof dissolving it. It adheres firmly to the metal and is of such a character that paint, enamel, japan,- lacquer, varnish or similar finishing-coat is strongly held by it. As the surface produced by my process tends to retard the rustin of the metal, it materially assists the finis to resist corrosion and therefore increases the life of the applied finish. As cellulose lacquers hold well to the coating produced as described above the usual metal oil. priming coat may be omitted and ,as such primers require a longfidrying "period'much time is saved in finis ng the metal whenmy process is used.

What I claim as'my invention is:

1. The method gf preparing metal for receiving a 'eoat co'nsisting'in coating the metal with phosphoric acid, retaining the acid on'the metal for a predetermined time to form a coating 'of water soluble metallic phosphate and thereafter rendering thesaid 0a., A. n. 1928.

coating of metallic phosphate adherent to the said metal and insoluble in water. i

2. The method of preparing metal for receiving a finishing adherent coat consisting in coating the metal with an admixture comprising phosphoricacid and an oil solvent,

and insoluble in water.

4. The method of preparing steel for receiving an adherent finishing coat consisting in coating the metal with phosphoric acid, retaining the said acid on the metal tier a predetermined time to form a coating of soluble metal phosphate and thereafter treating the said coating with s'laked' e for rendering the said coating adhere t and insoluble in water. I

5. The method of preparing metal for receiving an adherent coat consisting coating the metal with phosphoric acid to form a coating of soluble iron phosphate and there after treating the said coating with an admixture comprising slaked lime, water, cellulose pulpwaste liquor and butyl alcohol for rendering the said coating adherent and insoluble in water.

6. The methodof preparing steel -for receiving an adherent coat consisting in coating the metal with phosphoric acid to form a coatin of water soluble metal phosphate,

rendermg the said coating adherent and insoluble in water by coating the metal with a semi-fluid material. adapted to neutralize phosphoric acid. i

7. The method of preparing steel for painting consisting-in coatinglthe metal with an admixture comprising; p osphoric acid and an alcohol, retaining the said admixture on the metal under the influence of heat for a predetermined time to form a coatin of $0111- ble iron phos hate, rendering the sai coating adherent an insoluble in water b treating the said coating with a semi-flui material comprising an admixture of, which one ingre- III Ill

dient is slaked lime, drying the said material 11111 vin the said dried material together with t e on" the said coating and mechanically re-. I de eterious products of its Signed at New York, in the county of New York and State of New. York, this 1st day of Jms n. GBAVELL. 

